Science Advances 4, eaat7189

Science Advances 4, eaat7189 (2018)

Hexagonal boron nitride has been proposed as an excellent candidate to achieve subwavelength infrared light
manipulation owing to its polar lattice structure, enabling excitation of low-loss phonon polaritons with
hyperbolic dispersion. We show that strongly subwavelength hexagonal boron nitride planar nanostructures
can exhibit ultra-confined resonances and local field enhancement. We investigate strong light-matter interaction
in these nanoscale structures via photo-induced force microscopy, scattering-type scanning near-field optical microscopy,
and Fourier transform infrared spectroscopy, with excellent agreement with numerical simulations. We
design optical nano-dipole antennas and directly image the fields when bright- or dark-mode resonances are excited.
Thesemodes are deep subwavelength, and strikingly, they can be supported by arbitrarily small structures.We believe
that phonon polaritons in hexagonal boron nitride can play for infrared light a role similar to that of plasmons in noble
metals at visible frequency, paving the way for a new class of efficient and highly miniaturized nanophotonic devices.